A variety of materials are commonly used in the field of dental treatment, including impression materials, filling materials, and adhering materials. Often, these materials are formed at or near the time of use from a combination of two or more kinds of component materials. For example, dentists or dental technicians may remove required amounts of the component materials from their respective containers (for example, by weight, volume or length) and place these on a mixing pad to be mixed with each other and put into use. These mixed materials may then be placed in a cartridge suitable for application using a dispenser. In other cases, non-composite and pre-mixed dental materials may be directly provided by manufacturers in dispenser cartridges.
Conventional dispensers may use a variety of means for extruding these mixed materials from a cartridge. For example, a pistol-shaped cartridge dispenser maybe used that positions the cartridge in a predetermined position at the front of the device, and employs a piston coupled to a push rod for pressing against the mixed material from an opening in the rear of the tube in order to extrude the mixed material from a nozzle positioned at the front of the tube. The piston and push rod typically move in response to a mechanical force directly applied to the dispenser by a human operator, and may alternatively move in response to a force applied by other means (for example, supplied by a pressurized fluid or electric motor).
When operating such dispensers, it is desirable to precisely control the amount of material that is extruded. If an excess of material is supplied (over-extruded), for example, the dentist or dental technician will be required to remove the over-extruded material. This creates additional work for the dentist or dental technician, and may be difficult, for example, if the extruded material is a composition that hardens quickly once extruded. Removing over-extruded material may also create discomfort and or unwanted delay for the dental patient. In particular, it is desirable to avoid continued extrusion of material from the dispenser after actuation ceases (“drooling”).